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.Dd March 22, 2019
.Dt VOP_FSYNC 9
.Os
.Sh NAME
.Nm VOP_FDATASYNC ,
.Nm VOP_FSYNC
.Nd flush file system buffers for a file
.Sh SYNOPSIS
.In sys/param.h
.In sys/vnode.h
.Ft int
.Fn VOP_FDATASYNC "struct vnode *vp" "struct thread *td"
.Ft int
.Fn VOP_FSYNC "struct vnode *vp" "int waitfor" "struct thread *td"
.Sh DESCRIPTION
.Fn VOP_FSYNC
ensures that a file can be recovered to its current state following a crash.
That typically requires flushing the file's dirty buffers, its inode, and
possibly other filesystem metadata to persistent media.
.Fn VOP_FSYNC
is used to implement the
.Xr sync 2
and
.Xr fsync 2
system calls.
.Pp
Its arguments are:
.Bl -tag -width waitfor
.It Fa vp
The vnode of the file.
.It Fa waitfor
Whether the function should wait for I/O to complete.
Possible values are:
.Bl -tag -width MNT_NOWAIT
.It Dv MNT_WAIT
Synchronously wait for I/O to complete.
.It Dv MNT_NOWAIT
Start all I/O, but do not wait for it.
.It Dv MNT_LAZY
Push data not written by file system syncer.
.El
.It Fa td
The calling thread.
.El
.Pp
.Fn VOP_FDATASYNC
is similar, but it does not require that all of the file's metadata be flushed.
It only requires that the file's data be recoverable after a crash.
That implies that the data itself must be flushed to disk, as well as some
metadata such as the file's size but not necessarily its attributes.
.Fn VOP_FDATASYNC
should always wait for I/O to complete, as if called with
.Dv MNT_WAIT .
.Fn VOP_FDATASYNC
is used to implement
.Xr fdatasync 2 .
.Sh LOCKS
The vnode should be exclusively locked on entry, and stays locked on return.
.Sh RETURN VALUES
Zero is returned if the call is successful, otherwise an appropriate
error code is returned.
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er ENOSPC
The file system is full.
.It Bq Er EDQUOT
Quota exceeded.
.El
.Sh SEE ALSO
.Xr vnode 9
.Sh AUTHORS
This manual page was written by
.An Doug Rabson .
